Nevin Yagci

Characteristics of mixed microbial culture at different sludge ages: Effect on variable kinetics for substrate utilization

The study focused on variable kinetics for substrate utilization, primarily addressing the following issue: Is variable process kinetics observed under different operating conditions and culture history (sludge ages), the result of changes inflicted on the metabolic machinery of the same microbial culture? Or, is this the result of a different microbial population selected under different operating conditions? For this purpose, the study mainly emphasized to assess the microbial population composition sustained at different sludge ages. It explored the relationship between observed process kinetics and microbial population structure using respirometric modeling and high-throughput sequencing of 16S rRNA gene. Experimental results indicated a significant change in the composition of the microbial community fed with the same organic substrate, when the culture history was changed, lower sludge age selecting a different and faster growing microbial community.

Mechanism and design of intermittent aeration activated sludge process for nitrogen removal.

The paper provided a comprehensive evaluation of the mechanism and design of intermittent aeration activated sludge process for nitrogen removal. Based on the specific character of the process the total cycle time, (T C ), the aerated fraction, (AF), and the cycle time ratio, (CTR) were defined as major design parameters, aside from the sludge age of the system. Their impact on system performance was evaluated by means of process simulation. A rational design procedure was developed on the basis of basic stochiometry and mass balance related to the oxidation and removal of nitrogen under aerobic and anoxic conditions, which enabled selected of operation parameters of optimum performance. The simulation results indicated that the total nitrogen level could be reduced to a minimum level by appropriate manipulation of the aerated fraction and cycle time ratio. They also showed that the effluent total nitrogen could be lowered to around 4.0 mgN/L by adjusting the dissolved oxygen set–point to 0.5 mg/L, a level which promotes simultaneous nitrification and denitrification.

The investigation and assessment of characteristics of waste activated sludge after ultrasound pretreatment

In this study, the characteristics of sonicated waste activated sludge (WAS) originating from a nutrient‐removal wastewater treatment plant were investigated and evaluated. Different combinations of power inputs, sonication durations and volumes were used for optimization of the sonication conditions. Ultrasound density levels ranged between 0.32 and 3.2 W/mL. Optimal conditions based on soluble COD concentrations (SCOD) after sonication at different ultrasound density levels and sonication durations (1, 5, 10 and 30 min) were determined. An ultrasonic density of 1.6 W/mL and a sonication time of 30 min were identified as optimal sonication conditions in terms of SCOD concentration. The sludge sonicated under these optimal conditions was further investigated to determine the effect of ultrasound treatment on solubilization of organic matter and volatile solids, particle size and biodegradability. Disruption of the sludge structure was confirmed by the increase in the SCOD by 35.5%, reduction in volatile suspended solids by 26% and reduction in particle size by 85%. The availability of COD fractions of sonicated sludge was also tested with oxygen uptake rate and phosphate release data indicating that using sonicated sludge for both subsequent biological treatment and sludge treatment is promising.

Design of Sequencing Batch Reactors for Biological Nitrogen Removal from High Strength Wastewaters

Abstract This paper covers an evaluation of more than twenty full-scale industrial wastewater treatment plants employing sequencing batch reactor (SBR) process mainly for carbon removal and a pilot-scale SBR designed for carbon and nitrogen removal from tannery effluent. The study highlights the major features of the SBR technology and proposes a rational dimensioning approach for carbon and nitrogen removal SBRs treating high strength industrial wastewaters based on scientific information on process stoichiometry and modeling, also emphasizing practical constraints in design and operation.

The Effect of Nitrate and Different Substrates on Enhanced Biological Phosphorus Removal in Sequencing Batch Reactors

Abstract Enhanced biological phosphorus removal (EBPR) requires an anaerobic-aerobic sequence and short chain fatty acids, namely acetate. It is also known that the presence of nitrate in the anaerobic phase inhibits EBPR. This study describes a lab-scale experimentation carried out to study the effect of different substrates on EBPR and behaviour of PAOs under anoxic conditions in a sequencing batch reactor operated using synthetic wastewater. Experimental data show that the EBPR performance is significantly affected by glucose rich influent. Low COD/TKN ratios caused lower phosphorus removal performance since nitrate entering the anaerobic zone consumes substrate for denitrification. The results also show that anoxic phosphate uptake took place together with nitrate reduction when there was no external substrate. However, the uptake rate under anoxic conditions was lower than that under aerobic conditions.

The effect of iron dosing on reducing waste activated sludge in the oxic-settling-anoxic process

This study evaluates the biological solid reduction in a conventional activated sludge system with an anoxic/anaerobic side stream reactor receiving 1/10 of return sludge mass. Influent iron concentrations and feeding modes were changed to explore the consistency between the influent iron concentration and yield values and to assess the impact of feeding pattern. The results indicated that sludge reduction occurs during alternately exposure of sludge to aerobic and anoxic/anaerobic conditions in a range of 38-87%. The sludge reduction values reached a maximum level with the higher iron concentrations. Thus, it is concluded that this configuration is more applicable for plants receiving high iron concentrations in the wastewaters.

Effects of pH and substrate on the competition between glycogen and phosphorus accumulating organisms

Abstract This article evaluates effects of pH and substrate on the competition between glycogen (GAOs) and phosphorus accumulating organisms (PAOs). A sequencing batch reactor system was operated for enhanced biological phosphorus removal (EBPR) with acetate as the sole carbon source and acetate added domestic wastewater at different influent acetate/phosphate ratios. Some batch tests were performed using acetate added domestic wastewater at different influent acetate/phosphate ratios, with different initial pH values of acetate and domestic wastewater mixture. The resulting experimental data supported the presence of GAOs for all tested HAC/P ratios, especially under P limiting conditions for acetate as sole carbon source. Strong evidence is observed that acetate added domestic wastewater system had higher PAOs fraction than acetate system as sole source carbon, with using model components, namely substrate uptake, glycogen utilization and P release.

Experimental evaluation and model assessment of coexistence of PAOs and GAOs

The study evaluated the competition and co-existence of PAOs and GAOs in sequencing batch reactor (SBR) systems sustaining enhanced biological phosphorus removal (EBPR). The SBR operation used acetate as the sole external carbon source and covered a wide range of initial COD/P ratios between 6.5 to 25.9 g COD/g P. A mechanistic model, ASMGG, was adopted for this purpose, which basically incorporated model components and processes associated with GAO metabolism and glycogen metabolism of PAOs. Model calibration was successfully performed with the same set of stoichiometric and kinetic coefficients for all the acetate, phosphate, glycogen and PHA profiles obtained in different experiments. Interpretation of experimental results by means of model simulation indicated competition and co-existence of PAOs and GAOs within the EBPR process, numerically assessing the composition of the microbial community sustained and identifying the respective role and function of PAOs and GAOs on the fate of glycogen and PHA.

Effect of acetate to biomass ratio on simultaneous polyhydroxybutyrate generation and direct microbial growth in fast growing microbial culture

The study investigated the effect of variations in the acetate to biomass ratio on substrate storage potential, and the kinetics of substrate utilization. A series of batch experiments were conducted with biomass taken from the fill and draw reactor operated at a sludge age of 2 d. One of the batch reactors duplicated the substrate loading in the main reactor. The others were started with different initial acetate to biomass ratios both in lower and higher ranges. Increasing available acetate did not totally divert excess substrate to storage; the microbial culture adjusted the kinetics of the metabolic reactions to a higher growth rate so that more substrate could be utilized for direct growth at high acetate levels. Conversely, storage rate was increased, utilizing a higher substrate fraction for polyhydroxybutyrate generation when acetate concentration was lowered. The physiological and molecular bases of storage at low substrate levels were discussed.

COD fractionation and denitrification potential of sonicated waste activated sludge liquids

This study characterized sonicated waste activated sludge (WAS) liquids as a possible carbon source for nitrogen removal. In this context, the effect of sonication density on chemical oxygen demand (COD) and nitrogen release was determined by particle size distribution (PSD) analysis and anoxic batch experiments. The increase in ultrasonic density from 0.8 W/mL to 1.6 W/mL had a slight impact on the soluble COD/total COD ratio. The high ultrasonic energy input increased the solubilization of nitrogenous organic substances and resulted in a low COD/TKN (total Kjeldahl nitrogen) ratio, which is not appropriate for nutrient removal systems. The change in ultrasonic power had a significant effect on COD fractionation of sonicated WAS liquid. The COD fraction at the size ranges higher than 1600 nm decreased from 44% to 3% as the energy input increased. The increase in specific energy raised the COD fraction, at the size ranges of<2 nm, from 11% to 23%.The PSD-based COD fractionation showed that increasing the sonication density markedly changed the size distribution. The anoxic batch tests indicated that the specific denitrification rate of sonicated WAS liquid was in the range of that reported for the slowly biodegradable fraction of the domestic wastewater and higher than those reported for agro-food wastewater.